This invention relates to an apparatus for monitoring optical fiber connections, and, more particularly, for ascertaining stray optical radiation from the connector and surrounding neighborhood.
In optical fiber connection systems, essential components of virtually all such systems are fiber connectors which transmit optical energy from one fiber end to another, or to other active or passive devices. Such connections bear directly upon the amount of optical energy transmitted, and, as a consequence, there are numerous prior art arrangements for monitoring the amount of energy transmitted by and through a connection. For instance, in U.S. Pat. No. 5,793,909 of Leone et al. there is shown an optical monitoring and test access module for use in an optical fiber distribution frame or cross-connect frame having a multiplicity of fiber connects. The module monitors the optical signal level in a fiber line by tapping off a part of the signal and converting it to an electrical signal which, through subsequent processing, generates control signals when the power level of the received signal reaches certain specified levels. In U.S. Pat. No. 5,461,693 of Pimpinella there is shown an arrangement which launches test signals through a jumper cable from one connector module to another module connected to the first module by the jumper cable and which includes means for receiving and monitoring the test signal. In some arrangements, the receiving optical fiber, for example, is disconnected from its remote destination and connected to a power monitor which then monitors the signals, most often a test signal being transmitted. Such an arrangement requires an interruption in service, which is highly undesirable. On the other hand, the systems of the aformentioned patent to Leone et al. does not require service interruption, but does require extracting at least some of the transmitted power. Thus, most of the prior art arrangements are invasive in that they require presence of a signal through the connections being tested and operate by extracting some of the signal. In addition, such systems generally rely on bulk optics, complex circuitry, and, in many cases, require signal splitters, which, when used, impart unidirectionality to the monitor circuit.
Most prior art circuits are concerned with power monitoring or fault finding, or both. There is, however, in addition to these desiderata, another parameter which needs to be monitored, not only for efficiency of power transmission, but for safety for personnel in the vicinity of the connection or connections being monitored.
The connectors used in, for example, joining fiber ends have, as their primary function, the maintenance of the fiber ends in a butting relationship such that the core of one of the fibers is axially aligned with the core of the other fiber so as to maximize light transmission from one fiber to the other. Such alignment is extremely difficult to achieve, which is understandable when it is recognized that the mode field diameter of, for example, a single mode fiber is approximately nine microns (9, xcexcm or 0.009 mm.) Good alignment of the fiber ends (low insertion loss) is a function of the alignment, the width of the gap (if any) between the fiber ends, and the surface condition of the fiber ends, all of which, in turn are inherent in the particular connector design. In the present day state of the art there are numerous, different connector designs in use for achieving low insertion loss and stability. In most of these designs, a pair of ferrules (one in each connector), each containing an optical fiber end, are butted together end to end and light travels across the junction. Zero insertion loss requires that the fibers in the ferrules be exactly aligned, a condition that, given the necessity of manufacturing tolerances, and cost considerations, is virtually impossible to achieve except by fortuitous accident. In U.S. patent application Ser. No. 09/363,906 of Andrews et al., filed Jul. 28, 1999, which issued as U.S. Pat. No. 6,287,018 on Sep. 11, 2001, the disclosure of which is incorporated herein by reference, there is shown a connector which is tunable for achieving maximum possible signal transmissivity or minimum insertion loss. The ferrule-barrel assembly of that connector is incrementally rotatable to any of a plurality of positions which, when rotated by means of a special tool, places the connector configuration in the best possible position for transmission.
Even though insertion loss is reduced for the particular connector being tuned, especially when mated with a similarly tuned connector, there almost invariably remains a certain amount of ferrule (or fiber within the ferrule) central axis offset and, consequently, light scattering at the junction of the two ferrules which can produce a dangerous condition for personnel in the vicinity. This scattering can be especially great where the connectors are not tuned, or where the mismatch is particularly bad. As is most often the case, there will be a plurality of connectors mounted in jack housings, or receptacles which are panel mounted, as shown in U.S. Pat. No. 5,274,729 of King et al. and, where several connectors are mismatched sufficiently to produce light scattering, the light radiation, which is cumulative, can be quite dangerous.
The present invention comprises an apparatus and circuitry for non-invasively monitoring the amounts of scattered radiation from one or more connectors, and for indicating when a potentially dangerous condition exists.
In greater detail, the connector jack housing has a photo-diode mounted thereon for detecting the presence of scattered light and producing an electrical signal indicative thereof, the signal being proportional to the amount of light scattering. In a first embodiment of the invention, circuitry, which may be mounted on a small printed wiring board, converts the electrical current from the photodiode to a voltage which can then be applied to a suitable signaling device, such as an LED. The circuitry includes a comparator which has a reference voltage level to which the voltage from the photo-diode is compared. A first LED, which may emit a green light, for example, is lit as long as the comparator level is not exceeded. If the comparator level is exceeded, the green LED is deactivated and a red LED lights up, indicating either a line in use or a dangerous level of scattered light. Instead of the red LED, or in addition thereto, in extreme cases, the comparator output can be used to deactivate the faulty connection. The arrangement is bi-directional in that if either cable, for example, is disconnected, if there is light transmission in the remaining cable (or fiber) the apparatus will indicate the presence of that light. The invention does not, therefore, rely on unidirectional devices such as signal splitters.
In another embodiment of the invention, an attenuator for introducing a known amount of loss can be positioned, for example, between the two fiber ends in the connection, and used to guide the light to the photo-diode. Such an arrangement insures that there will always be an LED activated, the absence of which can then be used as an indication of a malfunctioning connection.
In both embodiments, the circuitry can be used to measure the optical power passing through the connection, where desired, without dependence upon signal direction. In addition, the photo-diode can be sensitive enough, and preferably is, to respond to even small amounts of light transmission through the connection to indicate that the connection should not be broken.
The various features and the principles of the present invention will be more readily apparent from the following description, read in conjunction with the drawings.